1. Field of the Invention
The present invention relates to a spread illuminating apparatus, and more particularly to a spread illuminating apparatus used as an illuminating means for a liquid crystal display device.
2. Description of the Related Art
A liquid crystal display (hereinafter, referred to as xe2x80x9cLCDxe2x80x9d) featuring low power consumption, low profile and light weight has been extensively used in electric products including cellular phones and personal computers.
However, since a liquid crystal, which is a structural element of the LCD, does not emit light by it self unlike a light emitting element such as a CRT, the LCD requires a separate illuminating means in order to observe an image. Recently, to satisfy the demand for downsizing and energy saving, a sheet-like spread illuminating apparatus of side light type (light conductive plate type) is often used.
An example of a spread illuminating apparatus of side light type is shown in FIG. 9.
In FIG. 9, a spread illuminating apparatus 1 is generally constituted such that a lamp 4 is disposed along and close to an end surface 3 of a light conductive plate 2 made of a light-transmissible material. The light conductive plate 2 is shaped rectangular and has a light reflection pattern 5 formed on a major surface thereof.
The lamp 4 is generally composed of a light conductive bar 6 shaped like a slim-rectangular-prism, made of a transparent material and arranged with a surface 6a along and close to the end surface 3 of the light conductive plate 2, and a spot-like light source 7 arranged to face an end surface of the light conductive bar 6.
The light conductive bar 6 has an optical path conversion means 8 formed on a side surface 6b thereof opposite to the side surface 6a facing the end surface 3 of the light conductive plate 2. The optical path conversion means 8 comprises a plurality of grooves 9, for example, triangular in section, extending in a direction of thickness of the light conductive bar 6, and arrayed in a longitudinal direction of the light conductive bar 6 (hereinafter, referred to as xe2x80x9cstair-like typexe2x80x9d) and makes light emitted from the spot-like light source 7 incident in a substantially uniform manner on the end surface 3 of the light conductive plate 2. In order to make the light to uniform, the triangular grooves 9 have their depths gradually increased in proportion to an increase in the distance from the spot-like light source 7.
Also, the spread illuminating apparatus 1 includes a frame 10 substantially U-shaped in section, having a predetermined width L1 and having a light reflection member (not shown) on its inner surface, and covers longitudinal surfaces of the light conductive bar 6 except the side surface 6a facing the light conductive plate 2, and an end portion (two surfaces toward the end surface 3 of the light conductive plate 2), thereby recovering light leaking from the light conductive bar 6 to improve the usability of the light.
The frame 10 is adapted also to securely hold together the light conductive bar 6 and the light conductive plate 2 with a predetermined strength.
Recently, the above-described spread illuminating apparatus is strongly demanded to have as large a liquid crystal screen area as possible. Accordingly, the frame is requested to have its portion minimized which covers the liquid crystal screen, and to meet this request in a compact configuration.
In the prior art shown in FIG. 9, if the width L1 of the frame 10 is decreased to comply with the above request, the covered area at the light conductive plate 2 is reduced making it difficult to securely hold together the light conductive bar 6 and the light conductive plate 2.
Under the circumstances, the present applicants have proposed a spread illuminating apparatus in Japanese Patent Application 2001-8966, in which the covered portion over the liquid crystal screen is minimized and the light conductive bar and the light conductive plate are strongly held together, while miniaturization is achieved. A spread illuminating apparatus 1A proposed in the above application includes a light conductive bar 20 and a light conductive plate 21 as shown in FIG. 10. The light conductive bar 20 is wedge-shaped and has a larger end surface 20a facing a spot-like light source 7. The light conductive plate 21 has an inclination angle (inclination angle on a light conductive plate) xcex2, which is an obtuse angle formed between an end surface 21 of the light conductive plate 21a facing the light conductive bar 20 and a side surface 21b thereof flush with the end surface 20a facing the spot-like light source 7. The light conductive bar 20 has an inclination angle (inclination angle of the light conductive bar) xcex1, which is an acute angle formed between a side surface 20b of the light conductive bar 20 facing the light conductive plate 21 and the surface 20a facing the spot-like light source 7.
In the apparatus shown in FIG. 10, when the light conductive plate 21 and the light conductive bar 20 are held together by the frame 10 (see FIG. 9), since the light conductive bar 20 is wedge-shaped, the frame 10 has a sufficiently large area to cover the light conductive plate 21 toward an end surface 20c of the light conductive bar 20 opposite to the end surface 20a facing the spot-like light source 7. Therefore, even when the width of the frame 10 is decreased, the frame 10 retains a sufficient strength to hold together the light conductive bar 20 and the light conductive plate 21, whereby the apparatus can be successfully downsized with an increased liquid crystal screen.
The optical path conversion means formed on the light conductive bar may comprise a plurality of grooves 20e and a plurality of flat portions 20f each connecting adjacent grooves 20e as shown in FIG. 11 rather than the stair-like type shown in FIG. 10.
However, in the prior art shown in FIGS. 9 to 11, the side surface 20b of the light conductive bar 6 facing the light conductive plate 21 and a side surface 20d opposite to the surface 20b come closer to each other as approaching the end surface 20c which is smaller than the end surface 20a. Therefore, when light introduced into the light conductive bar 20 through the end surface 20a travels toward the end surface 20c while repeating reflection at the side surface 20b and the side surface 20d (flat portions 20f), the angle of reflection decreases at each reflection, becomes smaller than the critical angle before the light reaches the end surface 20c, and exits out (leakage light) from the side surface 20b as shown in FIG. 12. In other words, the light introduced into the light conductive bar 20 from the surface 20a cannot sufficiently travel up to the end surface 20c, that is, the light cannot be sufficiently kept in the light conductive bar 20, thereby decreasing the luminance of the spread illuminating apparatus. This is also the case with the light conductive bar with the optical path conversion means of stair-like type.
In this connection, the present applicants proposed a spread illuminating apparatus, in which a plurality of wedge-shaped light conductive bars are arranged in parallel along the end surface of the light conductive plate in Japanese Patent Application No. 11-232652 (Japanese Unexamined Patent Application publication No. 2001-57106).
This spread illuminating apparatus still has the same problem as the prior art shown in FIG. 12 in that the leakage light is generated.
A spread illuminating apparatus with a wedge-shaped light conductive bar capable of forwarding light all the way up from one end surface to the other end surface thereof (keeping light therein) is disclosed in U.S. Pat. No. 5,894,539. The spread illuminating apparatus generally includes a wedge-shaped light conductive bar 20B as shown in FIG. 13. The light conductive bar 20B has a plurality of flat portions 25 stepped from one another and parallel to a side surface 20b facing a light conductive plate.
In the apparatus shown in FIG. 13, since the side surface 20b facing the transparent substrate is parallel to each of the flat portions 25, the reflection angles formed by the surface 20b and the flat portions 25 larger than the critical angle, thereby improving the luminance of the apparatus.
In the apparatus shown in FIG. 13, in which the light conductive bar 20B is arranged with the side surface 20b facing the transparent substrate (not shown), the light conductive bar 20B has a large end surface 20a, which makes a side surface 20d opposite to the side surface 20b positioned far apart from the light conductive plate thereby preventing a miniaturization of the apparatus. Also, when the light conductive bar 20B and the light conductive plate are to be held together by the frame 10 (see FIG. 9), the width of the frame 10 has to be large enough to cover the dimension equal to the end surface 20a and the end portion of the light conductive plate. This increases the size of the frame 10, resulting in an increased size of the whole apparatus.
The present invention has been made in the light of the above, and its object is to provide a downsized spread illuminating apparatus capable of reducing leakage light.
A spread illuminating apparatus according to a first aspect of the present invention comprises a quadrangular light conductive plate made of a light-transmissible material and a lamp having a light conductive bar made of a transparent material and arranged along an end surface of the light conductive plate, a spot-like light source arranged at an end surface of the light conductive bar. In the apparatus, the light conductive plate has an inclination angle, which is an obtuse angle formed by an end surface facing the light conductive bar with respect to a side surface flush with the end surface of the light conductive bar, the light conductive bar is wedge-shaped, has a large thickness toward the end surface and a small thickness toward the other end surface, and has an inclination angle, which is an acute angle formed by a side surface facing the light conductive plate with respect to the end surface, and a plurality of flat portions substantially parallel to the side surface facing the light conductive plate are formed on a side surface of the light conductive bar opposite to the side surface facing the light conductive plate, are connected to one another via each of a plurality of inclined surfaces descending toward the other end surface, and gradually step down with respect to the side surface facing the light conductive plate from the end surface toward the other end surface, thereby forming a stair-like configuration.
A spread illuminating apparatus according to a second aspect of the present invention comprises a quadrangular light conductive plate made of a light-transmissible material and a lamp having a light conductive bar made of a transparent material and arranged along an end surface of the light conductive plate, and a spot-like light source arranged at an end surface of the light conductive bar. In the apparatus, the light conductive plate has an inclination angle, which is an obtuse angle formed by the end surface facing the light conductive bar with respect to side surface flush with the end surface of the light conductive bar, and the light conductive bar is wedge-shaped, has a large thickness toward the end surface and a small thickness toward the other end surface opposite to the end surface, has an inclination angle, which is an acute angle formed by a side surface facing the light conductive plate with respect to the end surface, and has a plurality of grooves and a plurality of flat portions formed on a side surface thereof opposite to the side surface facing the light conductive plate, such that the flat portions are substantially parallel to the side surface facing the light conductive plate and each connect adjacent grooves.
According to a third aspect of the present invention, in the spread illuminating apparatus of the first or second aspect, an absolute value of a difference between an angle formed by the side surface of the light conductive bar facing the light conductive plate to a predetermined reference plane and an angle formed by the flat portions to the reference plane is 2xc2x0 or less, more preferably 1xc2x0 or less.
According to a fourth aspect of the present invention, in the spread illuminating apparatus of the first or second aspect, an angle formed by the side surface of the light conductive bar facing the light conductive plate with respect to the end surface is supplementary to the inclination angle of the light conductive plate.
A spread illuminating apparatus according to a fifth aspect of the present invention comprises a quadrangular light conductive plate made of a light-transmissible material, and a plurality of lamps each having a light conductive bar made of a transparent material and arranged in parallel along an end surface of the light conductive plate, and a spot-like light source arranged at an end surface of the light conductive bar. In the apparatus, each of a plurality of light conductive bars is wedge-shaped, has a large thickness toward the end surface and a small thickness toward the other end surface opposite to the end surface, and has an optical path conversion means formed on a side surface thereof opposite to the side surface facing the light conductive plate, an optical path conversion means of one light conductive bar disposed farthest from the light conductive plate is formed such that a plurality of flat portions substantially parallel to the side surface facing the light conductive plate are connected to one another via each of a plurality of inclined surfaces descending toward the other end surface so that the plurality of flat portions gradually step down with respect to the side surface facing the light conductive plate from the end surface toward the other end surface, thereby forming a stair-like configuration, and the shape combining the plurality of light conductive bars and the light conductive plate is generally rectangular.
A spread illuminating apparatus according to a sixth aspect of the present invention comprises a quadrangular made of a light-transmissible material and a plurality of lamps each having a light conductive bar made of a transparent material and arranged in parallel along an end surface of the light conductive plate, and a spot-like light source arranged at an end surface of the light conductive bar. In the apparatus, each of the plurality of light conductive bars is wedge-shaped, has a large thickness toward the end surface and a small thickness toward the other end surface opposite to the end surface, and has an optical path conversion means formed on a side surface thereof opposite to the side surface facing the light conductive plate, an optical path conversion means of one light conductive bar disposed farthest from the light conductive plate is formed such that a plurality of grooves are connected to one another via each of a plurality of flat portions, which are substantially parallel to the side surface facing the light conductive plate, and the shape combining the plurality of light conductive bars and the light conductive plate substrate is generally rectangular.
According to a seventh aspect of the present invention, in the spread illuminating apparatus of the fifth or sixth aspect, preferably, the plurality of light conductive bars are arranged in parallel such that the end surface with a large thickness and the other end surface with a small thickness are set alternately on the same side.
According to an eighth aspect of the present invention, in the spread illuminating apparatus of the fifth to seventh aspects, preferably, even-number pieces of lamps are arranged in parallel, and the light conductive plate is rectangular.
According to a ninth aspect of the present invention, in the spread illuminating apparatus of the fifth to seventh aspects, preferably, odd-number pieces of lamps are arranged in parallel, the light conductive plate has an inclination angle, which is an obtuse angle formed by the end surface facing the light conductive bar with respect to a side surface flush with the end surface of the light conductive bar positioned closest to the end surface of the light conductive plate, and the light conductive bar has an inclination angle, which is an acute angle formed by the side surface facing the light conductive plate with respect to the end surface facing the spot-like light source.